ZINC FOLDS THE N-TERMINAL DOMAIN OF HIV-1 INTEGRASE, PROMOTES MULTIMERIZATION, AND ENHANCES CATALYTIC ACTIVITY

The N-terminal domain of HIV-1 integrase contains a pair of His and Cy s residues (the HHCC motif) that are conserved among retroviral integr ases. Although His and Cys residues are often involved in binding zinc , the HHCC motif does not correspond to any recognized class of zinc b inding domain. We have investigated the binding of zinc to HIV-1 integ rase protein and find that it binds zinc with a stoichiometry of one z inc per integrase monomer. Analysis of zinc binding to deletion deriva tives of integrase locates the binding site to the N-terminal domain. Integrase with a mutation in the HHCC motif does not bind zinc, consis tent with coordination of zinc by these residues. The isolated N-termi nal domain is disordered in the absence of zinc but, in the presence o f zinc, it adopts a secondary structure with a high alpha helical cont ent. Integrase bound by zinc tetramerizes more readily than the apoenz yme and is also more active than the apoenzyme in in vitro integration assays. We conclude that binding of zinc to the HHCC moth stabilizes the folded state of the N-terminal domain of integrase and bound zinc is required for optimal enzymatic activity.